Look for favicon in .build or public

No argument is sent to express.favicon which means it defaults to ../public/favicon.ico relative to the favicon middleware. That's nice if you're using connect directly but in my case connect is found in the express folder. I guess I could just add the same version of connect to my dependencies, but that seems like a shaky and error prone solution. 

This PR looks in the root projects .build and public folders instead and defaults to no favicon if none is found which also solves #47.